FORWARD TWP — The weekend shooting death of 45-year-old Robert C. “Bob” Gaurrich at his auto repair shop remains a mystery. State police investigators acknowledged they have not settled on any suspects. “But we have people of interest,” Sgt. Patrick Sarnese said this morning. Police are also struggling to come up with a prevailing motive for the killing. A number of theories are being kicked around, Sarnese said. He would not elaborate. But there are other questions, like when Gaurrich was shot and the whereabouts of the gun used in the killing. “It’s a whodunit,” Butler County District Attorney Richard Goldinger said Tuesday. Gaurrich about 11 p.m. Friday was found dead behind his business, Bob‘s Truck and Auto Repair Service, on Route 68. An autopsy determined that he died of a gunshot wound to his chest. Police think he may have been fatally shot with a rifle, possibly his own older model .30- 30 rifle that he kept at his shop. Gaurrich had decided to sell the gun. “He had been showing it to different people,” Sarnese said. Authorities have been unable to find that missing firearm, which is described as an antique octagon barrel rifle, similar to a flintlock. The investigation has determined that Gaurrich was shot in the center of the building. He ran out the east side of the door before collapsing. “We’re still trying to narrow down when he was shot,” Sarnese said. Investigators have a rather wide time frame — somewhere between 4:30 and 11 p.m. Sarnese also said police have been reviewing personal and financial records of Gaurrich, hunting for clues that could help their investigation.